1. Field of Invention
The present invention relates to a light-emitting diode (LED) chip having a micro-lens structure, and more particular to an LED chip for providing a uniform plane light source.
2. Related Art
Referring to FIG. 1, the light-emitting chip having a micro-lens structure is a packaged LED chip 100, and it can be found from FIG. 1 that, an N-type semi-conductive layer 102, an active layer 104, and a P-type semi-conductive layer 106 are sequentially stacked on a transparent substrate 110. Then, the LED chip 100 is placed on a substrate 110 (e.g., a lead frame), and after the N-type semi-conductive layer 102 and the P-type semi-conductive layer 106 are respectively guided to two electrode points 116 and 118 of the substrate 110 through leads 112 and 144, a lens 120 is integrally packaged, and thus, an LED chip 100 is finished. The N-type semi-conductive layer 102 and the P-type semi-conductive layer 106 can be exchanged with each other.
When being used, as long as a current is applied on the two electrode points 116 and 118 of the substrate 110, light 122 is produced by the interaction of electrons and holes between the N-type semi-conductive layer 102 and the P-type semi-conductive layer 106 and the active layer 104. The wavelength of the light 122 is relevant to the material of the active layer 104. The produced light 122 is emitted by the lens 120 after being reflected and refracted, and thus, the lens 120 has both functions of guiding the light-emitting angle and protecting the chip.
Although the above structure is capable of producing lights, the direction of the light emitted from the lens is difficult to be controlled due to the internal total reflection and refraction, and a distribution diagram of the light-emitting angle and intensity shown in FIG. 2 is usually produced. As known from FIG. 2 that, the design of the lens 120 makes the light-emitting angle 124 (the angle for emitting the light) between about positive 35° and negative 35° from the central optical axis (0° position), and the closer the distance from the central optical axis is, the higher intensity is. As seen from FIG. 2 that, the region 128 having a higher intensity is about positive/negative 12° from the central optical axis, and thus, the uniformity of the light source is poor, and it is not suitable for the application requiring a plane light source.
FIG. 3 shows a technique of controlling the light emitting direction, which is disclosed in the U.S. Pat. No. 6,987,613. FIG. 3 shows a flip chip LED chip 130 with a Fresnel lens layer 134 added above a top layer 132. Therefore, the light 138 emitted from the active layer 136 performs a total reflection in the LED chip 130 (at the left side, right side, and lower side of the figure), and the light 138 is emitted from the light-emitting surface (the upper side of the figure) through the Fresnel lens layer 134. Since the Fresnel lens layer 134 is characterized in emitting the light in parallel (so-called parallel light), a plane light source is produced.
Although the above U.S. Pat. No. 6,987,613 can achieve the object of a plane light source, due to the complicated process for fabricating the Fresnel lens layer 134, it is difficult to be produced.
Moreover, FIG. 4 shows a technique of fabricating a lens on the surface from which the LED emits the light, which is disclosed in U.S. Pat. No. 7,023,022. It is characterized in disposing a micro-lens array layer 162 on a light-emitting surface of the LED chip 160, such that a total reflection does not occur when the light is emitted from the active layer 164 to the micro-lens array layer 162, but the light passes there through, so as to enhance the overall light-emitting performance. However, as for the direction of the light, it cannot provide a uniform plane light source.